Take a look at Michael Aschbacher's paper "On the maximal subgroups of the finite classical groups" in Invent. Math. 76 1984, 469-514. If you can't access it through your university, you could find on pages 3-4 of citeseerx.ist.psu.edu/viewdoc/… a statement of Aschbacher's theorem in case of the PGL that might be helpful for you.
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SomeoneJun 16 '11 at 15:42